This invention is concerned with the production of high purity radioiodine for thyroid measurement and as a general radionuclide. The invention is particularly directed to an improved target for bombarding .sup.122 Te or .sup.123 Te with a beam that is within the energy limitations of a cyclotron to produce .sup.123 I.
Radioactive iodine is used for medical diagnostic studies. The isotope .sup.131 I has been used for this purpose because of its availability. The radioisotope .sup.123 I is considered much superior to the .sup.131 I in studies where the amount of radiation exposure to a patient is of prime concern. The radiation exposure received by a patient from .sup.123 I is about 1/40th that of an equal amount of .sup.131 I because of the shorter half-life and the decay by electron capture.
The gamma ray energy of .sup.123 I is 159 KEV compared to 364 KEV for .sup.131 I. Collimators associated with gamma ray scanning devices operate more effectively with this lower energy. Also the collimators used with .sup.123 I are less bulky.
A method of .sup.123 I production is disclosed in copending application Ser. No. 863,280 which is now U.S. Pat. No. 3,694,313. This method uses a target assembly which includes a porous plate for supporting enriched tellurium powder target material in a compact cyclotron having a He.sup.3 beam at an energy up to 30 MEV. Conventional cyclotrons have He.sup.3 beams at energies up to about 76 MEV.
When bombarded with beams of 30 to 50 microamperes of alpha particles or He.sup.3 tellurium radiation damages. This target material gets so hot that it vaporizes and redeposits in cooler regions. This reduces the efficiency of .sup.123 I production.